Add viewer-range categories, nomination tracking, dynamic showact form, session timeout, share URLs, and workflow-per-season

Features:
- Category viewer ranges + subcategory templates (admin group modal, tree workspace)
- Nomination enrichment via TwitchTracker API (NominationEnrichmentService,
  TwitchTrackerViewerStatsProvider) with admin tracking rules editor
- Nomination group tracker: CategoryGroupName as primary identifier,
  CategoryId stays as nullable legacy field; StreamerIdentity table
- Dynamic showact application form builder (AdminShowactFormBuilder,
  ShowactApplicationSchedule)
- Session idle timeout setting (AdminSessionTimeoutCard)
- Share URLs for X and Discord (SiteSettings, public extras)
- Workflow rules now stored per season (falls back to global SiteSettings)
- New admin routes: settings/access, settings/workflows, tracking-rules
- New admin review workspace with subcategory tabs
- AdminCategoriesView rebuilt with group/subcategory modals

Migrations (all additive):
- AddShareUrls, AddShowactDynamicForm, AddCategoryViewerRanges,
  AddSessionIdleTimeoutSettings, AddSeasonSubcategoryTemplates,
  AddNominationGroupTrackerIdentity, AddShowactApplicationSchedule,
  AddSeasonWorkflowRulesJson

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Backend/Migrations/20260628205353_AddSeasonWorkflowRulesJson.cs

@@ -0,0 +1,36 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Backend.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddSeasonWorkflowRulesJson : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "WorkflowRulesJson",
+                table: "Seasons",
+                type: "text",
+                nullable: false,
+                defaultValue: "[]");
+
+            migrationBuilder.Sql(
+                """
+                UPDATE "Seasons"
+                SET "WorkflowRulesJson" = COALESCE(NULLIF((SELECT "WorkflowRulesJson" FROM "SiteSettings" WHERE "Id" = 1), ''), '[]')
+                WHERE COALESCE("WorkflowRulesJson", '') = '';
+                """);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "WorkflowRulesJson",
+                table: "Seasons");
+        }
+    }
+}